BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to fluorescent lamp operating circuits and, more particularly,
to an electronic fluorescent lamp operating circuit for starting and operating a fluorescent
lamp load at a controllable output level.
2. Description of the Prior Art
[0002] Presently, fluorescent lamp operating circuits for providing variable illumination
levels from fluorescent lamps have involved the use of chopping circuitry to limit
the overall electrical power delivered to the fluorescent lamp. Such circuits employ
high frequency signals during a portion of the a-c power wave, which create electromagnetic
interference having a deleterious effect upon the operation of electronic equipment
located in the vicinity of the ballast circuit or lamps and low power factor. The
prior art fluorescent lamp control circuits provided dimming of the level of illumination
by dissipating the energy within the power supply circuitry. This created heat which
had to be dissipated from the system and resulted in substantial inefficiencies in'terms
of light output versus electrical power input.
SUMMARY OF THE INVENTION
[0003] An object of the present invention is to provide a fluorescent lamp operating circuit
which allows reliable starting of fluorescent lamps and controllable operation of
the fluorescent lamps at a variety of illumination levels without reducing the overall
lighting system efficiency. A more specific object of the present invention is to
provide an electronic ballast circuit including control signal detection circuitry
for receiving control signals transmitted over the power line and adjusting the light
output according to the information contained in the control signal.
[0004] Accordingly, the present invention includes a bridge circuit for converting a standard
frequency power signal into a d-c input, an inverter circuit for converting the output
of the d-c signal to a high frequency a-c wave for providing power to a fluorescent
lamp load, an electrode heating control circuit for controlling the application of
heating current to the lamp electrodes, an input control circuit for controlling the
switching frequency of the transitors of the inverter circuit, a receiver circuit
for receiving high frequency control signals from the power line and decoding binary
messages from the control signals for providing control of the switching frequency,
and a power transformer for supplying high frequency lamp operating power to the fluorescent
lamp load including an auxiliary starting circuit for applying a starting voltage
to the load after preheat of the fluorescent lamp filament by an auxiliary power circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] Further objects and advantages of the present invention together with its organization,
method of operation and best mode contemplated may best be understood by reference
to the following description taken in conjunction with the accompanying drawings in
which:
Fig. 1 is a schematic circuit diagram illustrating the fluorescent lamp operating
circuit of the present invention; and
Fig. 2 is a schematic timing diagram illustrating the input control signals of the
circuit diagram of Fig. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0006] The fluorescent lamp operating circuit 10 of the present invention, as shown in Fig.
1, includes input terminals 12 and 14 for connection to a power supply system having
a signal generating and transmitting means attached to it for providing control signals
to the operating circuit 10. Such a signal generating and transmitting system is disclosed
in U. S. Patent Application Serial No. (LD 9607) filed concurrently herewith by William
M. Rucki and assigned to the present assignee which discloses and claims a system
for providing to a power line carrier control signals of the character utilized by
the fluorescent lamp operating circuit of the present invention. The circuit 10 of
the present invention includes a notch-filter 16 including capacitor C16, inductor
L2 and capacitor C15 connected as shown in the Fig 1. The output of the notch filter
is provided to a bridge rectifier circuit 18 including the four diodes D27, D28, D29
and D30. The bridge rectifier 18 supplies via capacitor Cl a rectified d-c signal
to the power factor correction circuit 20 which includes diodes Dl, D2, D3, zener
diode D27, resistors R8 and R15, SCR1, inductor Ll and capacitor C2 as shown in the
Fig. 1 connected to ground. The output of the power factor correction circuit 20 is
supplied to an inverter switch circuit 22 which includes transistor Ql supplied from
transformer T2 connected to a d-c power supply at the terminal 24 via resistor Rl
and capacitor C4 and connected to the transistor Ql via diodes D4 and D5 and resistor
R3 connected as shown with diode D8 connected across the output of transistor Ql;
and transistor Q2 supplied from transformer T3 having its primary winding supplied
from the d-c source 24 via resistor R2 and capacitor C3 and having a secondary winding
connected via diodes D6 and D7 and resistor R4 to the base of transistor Q2 as shown,
with diode D9 connected across the output of the transistor Q2. The inputs to the
transformers T2 and T3 are controlled by the outputs of IC3 connected respectively
at points A and B to be described hereinafter. The transistors Ql and Q2 are connected
in a half bridge arrangement with capacitors C6 and C7 as shown. The output from the
junction 26 between capacitors C6 and C7 is supplied to the primary winding of transformer
Tl whose secondary winding supplies power to the lamp load 28 across capacitor C10.
Also connected to the junction point 26 is a primary winding of the transformer T4
whose secondary windings are connected to the respective terminals of the lamps of
the lamp load 28 to provide preheating current to the lamp electrodes to assist in
starting the lamps. The numerals shown on the drawing at the respective ends of the
transformer windings are pin numbers for the electronic components comprising the
elements shown schematically in Fig. 1. The input from the notch filter 16 is also
connected to a bootstrap circuit 30 including diode D15 resistors R5, R6, and R12,
capacitor C8 and transistor Q4 connected as shown in Fig. 1. The output of the bootstrap
circuit 30 is connected to a power supply circuit 32 which includes a transformer
winding on the transformer T1 to operate as a secondary and includes diodes D17, D18,
D23, D24, D25 and D26; and capacitors C9 and C14 connected as shown in Fig. 1 to provide
a reference voltage at output terminal 34 for the control circuit to be described
hereinafter. A receiver circuit 36 is also connected to the input terminals 12 and
14 via blocking capacitor C26 and transformer T6 having capacitor C27 connected across
its output terminals. Integrated circuit IC4 is connected to transformer T6 via resistor
R16 at pin 10 and to capacitors C18, C19, C20, C21 and C25, resistors R17, R18, R19
and R20 and zener diode D16 at the respective pins as shown in Fig. 1. Integrated
circuit IC4 is connected to pin 2 of IC6 with filter capacitor C28 connected thereto
and IC6 is connected at pin 1 to the reference voltage output 34 of the power supply
circuit 32. Integrated circuit IC5 is connected to pin 12 of IC4 and has resistors
R21, R22, R23, and capacitors C22, C23, C24 and C29 connected to respective pins thereof
as shown in Fig. 1. The outputs from pins IC5 at 12, 13, 14 and 15 of IC5 are provided
to the respective pins 1, 2, 4, 5, 9, 10, 12 and 13 on integrated circuit IC7, for
the respective gates connected thereto having respective resistors R25, R26, R27 and
R28 connected to the output pins 3, 6, 8 and 11, respectively, thereof with filter
capacitor C17 connected to the opposite side of each of the respective resistors R25-R28.
A control circuit 38 includes integrated circuit IC3 for providing the control signals
A and B for the inverter switch circuits and has resistors R7, R9 and Rll, potentiometer
Pl and capacitors C11 and C13 connected thereto as shown in Fig. 1. The control circuit
38 also includes logic gates 40, 42, 44 and 46 disposed on an additional integrated
circuit IC2 resistors R10, R12, capacitors C5, C12, diodes D10, D11, D12, D13, D14,
transistor Q3 and diodes D19, D20, D21 and D22 connected to the primary winding of
transformer T7 whose secondary winding is connected in series with the primary winding
of the preheat transformer T4 to provide a control signal to the preheat circuits
for controlling the application of preheating current to the lamp electrodes. The
secondary winding of transformer T5 is connected electrically in series with the primary
winding of transformer T1 and has a center tapped primary winding connected to the
diodes D11 and D12 as shown in the figure to provide a control signal to turn on electrode
heat when the lamps are started.
[0007] The fluorescent lamp operating circuit illustrated in Fig. 1 operates as follows.
Upon application of a-c power, for example 277 volt a-c input at the terminals 12
and 14, the bootstrap circuit 30 provides a power signal to the power supply circuit
32 which generates a d-c reference voltage signal which is applied to the receiver
circuit at IC6. This then generates pluses at A and B of 38 firing Q1 and Q2 of 22
which generates a voltage on power supply 32 from transformer Tl. The bridge rectifier
provides a d-c signal to circuit 20 and the power factor correction circuit 20 supplies
a d-c power signal to the inverter switch circuit 22 when the 277 volt a-c signal
is near zero voltage. The output of the inverter switch circuit 22 at terminal 26
feeds the primary winding of the transformer Tl and the primary of transformer T4.
The transformer T4 which has a plurality of secondary windings connected to the respective
filaments at the ends of the respective fluorescent lamps to preheat the windings
to emissive temperatures. The output at terminal 26 also feeds the primary windings
of transformers Tl and T5. The secondary winding of transformer T5 provides an output
signal via diodes Dll and D13 to gate 40 which forces A and B to go to a high frequency
(65 KHz) when there is an overload condition on Ql and Q2. With either input of gate
44 going low, the output of 46 goes high which turns on transistor Q3 to apply a voltage
to the primary winding of transformer T7 to allow current flow through the primary
winding of transformer T4. The output of the transistors Ql and Q2 is at a frequency
of approximately 65 kilohertz and the component values of capacitors C10 and the inductances
of the secondary winding of the transformer Tl and the auxilary winding L7-12 are
selected so that at resonance C10 applies a high voltage across the series connected
lamps to initiate the arc and therefore start the lamps. To initiate the arc, the
frequency is reduced to 40 KHz which is the resonant frequency of the combination
of C10 and the secondary winding and auxiliary winding of transformer Tl.
[0008] A multi-bit binary control signal shown in Fig 2a is transmitted over the power line
as a high frequency, e.g. 125 KHz center frequency, signal and is received at the
input transformer T6. The secondary winding of transformer T6 and capacitor C27 form
a tuned circuit at the data transmission frequency so that the data signal is transmitted
to the integrated circuit IC4 which detects the binary signal and provides the series
multi-bit data signal shown in Fig. 2b to the decoder ICS. IC5 decodes the input signal,
stores the decoded data in memory and decodes the next data signal and compares the
two data values. If two consecutive data values are equal IC5 translates the data
into a multi-bit parallel binary output signal which is supplied via the gates on
IC7 to IC3 to cause integrated circuit IC3 to provide output frequency control signals
A and B to the windings of transformers T2 and T3 to control the switching frequency
of transistors Ql and Q2. In a sample circuit constructed as shown in Fig. 1, IC4
was a LM1983 frequency shift key transciever sold by National Semiconductor. Capacitor
C18 is a 60 Hz filter, and capacitors C19 and C20 are filter capacitors. Resistor
R17 and capacitor C25 set the center frequency of the voltage controlled oscillator
on IC 4. Resistor R18 and capacitor C21 comprise a phase locked loop filter and set
the system a-c gain. Resistor R19 ia a pull-up resistor on an open collector and resistor
R20 is a bias resistor for a transistor on IC4. When a data signal is received by
IC4, the frequency modulated data shown in Fig. 2a is decoded into a serial binary
data word and outputted at pin 12 of IC4 to serial input decoder ICS, e.g. a MC145027
sold by Motorola. IC5 has resistors R21, R22 and capacitors C23 and C22 connected
as shown to set the detection characteristics of ICS. IC5 detects a five bit address
code and if the address is correct, the four data bits are decoded and stored in a
data register on IC5 for comparison with the successive data word. If two successive
data words agree, a control signal of four parallel bits is transmitted to IC7, e.g.
a nand chip 74LS03 sold by Texas Instruments. Binary zeroes in the parallel data word
cause a current increase through resistor R9 to cause the frequency outputs of IC3
to vary at A and B. The frequency shift at A and B on transformers T2 and T3 shifts
the switching frequency of transistors Ql and Q2 to vary the voltage across capacitor
C10 and therefore the intensity of light output from lamps in the load 28.
1. An operating circuit for supplying electrical power to a fluorescent lamp load
comprising:
input means for receiving an a-c electrical power signal;
rectifier means for converting said a-c power signal to a d-c power signal;
controllable electrode heating current supply means for supplying electrode heating
current to the lamp electrodes fluorescent lamp starting means for applying a starting
voltage to a fluorescent lamp load;
frequency controlled power switching means connected to the output of said rectifier
means for converting said d-c power signal to a high frequency electrical signal for
supplying electrical power to the lamp load during normal operation thereof;
communication circuit means for receiving frequency modulated binary control signals
transmitted over said power line and translating said binary control signals into
variable current control signals dependent upon the value of said binary control signals;
and
control circuit means for receiving said current control signals and providing frequency
control signals to said high frequency power switching means for controlling the switching
frequency of said power switching means dependent upon said value of said binary control
signals.
2. The invention of claim 1 wherein said frequency controlled power switching means
comprises:
first and second bipolar power transistor means connected in a half bridge arrangement
to said output of said recitfier means;
first and second frequency controlled drive transformer means connected respectively
to the base terminals of said first and second power transistor means for controlling
the switching frequency of said first and second transistor means
3. The invention of claim 2 wherein said control circuit means comprises:
integrated circuit current controlled oscillator means for receiving said variable
current control signals and providing said frequency control signals whose frequency
depends upon the current value of said current control signals to said first and second
drive transformer means.
4. The invention of claim 3 wherein said communication circuit means comprises:
high frequency coupling transformer means for receiving said binary control signals
from said power line;
frequency shift key transciever means for detecting said frequency binary modulated
control signals and translating said frequency modulated binary control signals into
a serial binary data word; and
current control gate means for converting said binary control signals into current
control signals having a current level dependent upon the value of said binary control
signals.
5. The invention of claim 4 further comprising:
electrode heating control circuit means for applying electrode heating current to
said lamp electrodes dependent upon the value of said binary control signals.